Semiconductor fabrication processes often involve deposition of metals, such as tungsten, into features to form contacts or interconnects. As devices shrink, features become smaller and harder to fill, particularly in advanced logic and memory applications. Fabrication of metal contacts, metal interconnects, or other metal structures may involve etch back of the metal.
One aspect of the disclosure relates a method of etching a metal on a substrate, the metal being selected from tungsten (W) and cobalt (Co). It involves (a) exposing a surface of the metal to a halide chemistry to form a modified halide-containing surface layer; and (b) applying a bias voltage to the substrate while exposing the modified halide-containing surface layer to a plasma to thereby remove the modified halide-containing surface layer. In some embodiments, the plasma is an argon plasma and the bias voltage in (b) is between about 50 Vb and 80 Vb.
In some implementations, the modification operation of (a) includes exposing the surface of the metal to a plasma. If a plasma is used during (a), a bias may or may not be applied to the substrate during (a). The substrate temperature may be maintained to prevent spontaneously etching the metal. For example, in some embodiments, (a) involves exposing a tungsten surface to a chlorine-containing plasma at temperatures less than 150° C. to prevent spontaneous etch of the tungsten by the plasma.
Also provided is an apparatus for processing semiconductor substrates, the apparatus including: a process chamber comprising a showerhead and a substrate support, a plasma generator, and a controller having at least one processor and a memory, wherein the at least one processor and the memory are communicatively connected with one another, the at least one processor is at least operatively connected with flow-control hardware, and the memory stores machine-readable instructions for: (i) introducing a halide-containing gas to modify a tungsten surface; and (ii) introducing an activation gas and igniting a plasma to etch at least part of the modified surface of tungsten. In some implementations, the memory further stores machine-readable instructions for igniting a plasma during (i). In some embodiments, the halide-containing gas is a chlorine-containing gas and memory further stores machine-readable instructions for maintaining a temperature of the substrate support at less than 150° C. during (i).
These and other aspects of the disclosure are discussed further below.